Atmospheric Circulation of Hot Jupiters: Dayside-Nightside Temperature Differences. II. Comparison with Observations

TL;DR

This paper compares analytic and numerical models of hot Jupiter atmospheric circulation with observations, showing that wave propagation limits temperature differences at high flux, but cooler planets require additional effects like clouds or metallicity.

Contribution

It validates the analytic theory against observations and explores how circulation and temperature differences vary with stellar flux and drag, highlighting the need for additional effects at lower temperatures.

Findings

Analytic theory explains the trend of increasing temperature difference with stellar flux.

Numerical models show temperature differences increase with flux and drag.

Strong drag or additional effects are needed to match observed phase curves.

Abstract

The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing fractional dayside-nightside brightness temperature difference with increasing incident stellar flux, both averaged across the infrared and in each individual wavelength band. The analytic theory of Komacek & Showman (2016) shows that this trend is due to the decreasing ability with increasing incident stellar flux of waves to propagate from day to night and erase temperature differences. Here, we compare the predictions of this theory to observations, showing that it explains well the shape of the trend of increasing dayside-nightside temperature difference with increasing equilibrium temperature. Applied to individual planets, the theory matches well with observations at high equilibrium temperatures but, for a fixed photosphere pressure of $100 \ \mathrm{mbar}$, systematically under-predicts the dayside-nightside brightness temperature differences at equilibrium temperatures less than $2000 \ \mathrm{K}$. We interpret this as due to as the effects of a process that moves the infrared photospheres of these cooler hot Jupiters to lower pressures. We also utilize general circulation modeling with double-grey radiative transfer to explore how the circulation changes with equilibrium temperature and drag strengths. As expected from our theory, the dayside-nightside temperature differences from our numerical simulations increase with increasing incident stellar flux and drag strengths. We calculate model phase curves using our general circulation models, from which we compare the broadband infrared offset from the substellar point and dayside-nightside brightness temperature differences against observations, finding that strong drag or additional effects (e.g. clouds and/or supersolar metallicities) are necessary to explain many observed phase curves.